Effects of waterlogging and salinity on plant-water relations and on the accumulation of solutes in three mangrove species

Dispersal units of Avicennia marina (Forsk.) Vierh., Rhizophora mucronata Lam. and Bruguiera gymnorrhiza (L.) Lam. were cultivated in mangrove sediment under greenhouse conditions. After 7 months plants were subjected to the following waterlogging and salinity treatments for 60 days: drained non-saline, drained saline, waterlogged non-saline and waterlogged saline. Measurements were made of stomatal resistance (r_s), tissue water potentials, relative water content, and the concentration of Na, K, Ca and Mg in plant organs. Measurements were made 4 days before the termination of waterlogging and continued for 12 days thereafter. Generally, the highest stomatal resistance occurred in the waterlogged saline treatments and the least stomatal resistance occurred in the drained non-saline treatments. Water potentials were usually lower in the saline treatments than in the non-saline treatments. Depression in water potential was greatest in Avicennia and least in Bruguiera. In all 3 species, the concentration of cations was high in the roots. Salinity had greater effects on the concentration of ions in Avicennia than in Rhizophora or Bruguiera. The low stomatal resistance, low tissue water potentials, high relative water content and high tissue cation concentration in Avicennia suggest that it is ideally suited as the pioneer in the mangrove association. Generally, Rhizophora was more tolerant of salinity than Bruguiera. The responses of the plants reveal the remarkable adaptability of mangroves to the saline environment. The adaptive features of each species determine its characteristic habitat in intertidal areas.     

Does sea level rise influence propagule establishment, early growth and physiology of Kandelia candel and Bruguiera gymnorrhiza?

Responses of Kandelia candel and Bruguiera gymnorrhiza in loamy-sandy (coarse) and silty (fine) soils to water level rise and prolonged inundation were investigated under mesocosm and field conditions. Acidity due to simulated sea level rise of 30 cm was more serious in fine soil than that in coarse soil. Propagules of K. candel had more rapid establishments under high water level and prolonged inundation, but establishments of B. gymnorrhiza were not significantly influenced by tide condition. Water level rise of 30 cm and prolonged inundation stimulated early growth especially in stem height increments during the first 2 months for K. candel and B. gymnorrhiza. However, relative growth rates (RGRs) during the second 2 months did not significantly change for K. candel and even decreased for B. gymnorrhiza with water level rise. The root/shoot biomass ratio in both K. candel and B. gymnorrhiza treated with high water level was significantly lower than that treated with low water level, especially in coarse soil. Biomass percentages of coarse roots of K. candel and B. gymnorrhiza seedlings significantly increased with water level rise. Water level rise led to decreases in Chl. a/b ratios in leaves of K. candel seedlings, but the ratios did not significantly change with water level for B. gymnorrhiza. Decreases in RGRs of B. gymnorrhiza were due to decreases in total leaf area resulting from increases in stomatal density. Contents of N and P in roots tended to increase with water level rise and prolonged inundation. Under both high and low water levels, all propagules of K. candel and B. gymnorrhiza successfully established and the seedlings survived throughout the mesocosm experiment. For the field trial, K. candel seedlings had similar high survival rates of over 90%, while B. gymnorrhiza seedlings had much less survival in lower intertidal zones than in upper intertidal zones. These differences were ascribed to stronger tidal action and more sedimentation in the field than under mesocosm conditions. Survived seedlings of K. candel and B. gymnorrhiza from both propagule plantation and seedling transplantation in field trial also showed higher stem increments during the first 4 months in lower intertidal zones.     

Growth and physiological responses of Kandelia candel and Bruguiera gymnorrhiza to livestock wastewater

Growth and physiological responses of two mangrove species (Kandelia candel and Bruguiera gymnorrhiza) to livestock wastewater under two salinity conditions (seawater with salinity of 30þ and freshwater) were examined in greenhouse pot-cultivation systems for 144 days. Wastewater treatment significantly enhanced growth of Kandelia candel and Bruguiera gymnorrhiza in terms of stem height, stem basal diameter, leaf production, maximum unit leaf area and relative growth rate. Wastewater discharges and salinity levels did not significantly change biomass partitioning of Kandelia candel, however, more biomass of Bruguiera gymnorrhiza was allocated to leaf due to wastewater discharges. In Bruguiera gymnorrhiza, contents of chlorophyll a and chlorophyll b increased with wastewater discharges but such increase was not observed in Kandelia candel. On the other hand, livestock wastewater increased leaf electric conductance in Kandelia candel but not in Bruguiera gymnorrhiza. The peroxidase activity in stem and root of Kandelia candel under both salinity conditions increased due to wastewater discharges, while the activity in root of the treated Bruguiera gymnorrhiza seedlings decreased under freshwater condition but increased at seawater salinity. The superoxide dismutase activity in treated Bruguiera gymnorrhiza decreased but did not show any significant change in Kandelia candel receiving livestock wastewater.     

Chloroplast microsatellite markers for the mangrove tree species Bruguiera gymnorrhiza, Kandelia candel, and Rhizophora stylosa, and cross-amplification in other mangrove species

Chloroplast microsatellite (cpSSR) markers were developed for three ecologically and economically important tree species in the mangrove family, Rhizophoraceae: Bruguiera gymnorrhiza, Kandelia candel, and Rhizophora stylosa. Noncoding regions of chloroplast DNA (cpDNA) from each species were separately amplified using universal chloroplast primers. Six, two, and three polymorphic cpSSR loci in B. gymnorrhiza, K. candel, and R. stylosa, respectively, were developed from amplified noncoding cpDNA regions. Characterization of 216, 156, and 253 individuals of B. gymnorrhiza, K. candel, and R. stylosa, respectively, collected from different natural mangrove populations (B. gymnorrhiza, 9; K. candel, 7; R. stylosa, 9) on Iriomote Island in Japan showed that these loci provide cpSSR markers with polymorphisms ranging from two to four alleles per locus and gene diversity between 0.027 and 0.480. These cpSSR markers will be useful for analyzing the maternal lineage distributions and population genetic structures of the three species. Several of these markers may also be useful in similar studies of other mangrove species.     

不同生长光强下8种红树植物幼苗叶片的光响应特征

为探讨红树植物光适应的生理生态策略,对6种真红树植物[无瓣海桑(Sonneratia apetala)、秋茄(Kandelia candel)、木榄(Bruguiera gymnorrhiza)、桐花树(Aegiceras corniculatum)、老鼠簕(Acanthus ilicifolius)、卤蕨(Acrostichum aureum)]和2种半红树植物[银叶树(Heritiera littoralis)、黄槿(Hibiscus tiliaceus)]的1 a生幼苗在不同生长光强(自然光强的100%、45%、30%、10%)下的光合光响应特征进行了研究。结果表明,不同生长光强对红树植物光响应特征的影响因物种而异,遮荫显著提高了秋茄和木榄的最大净光合速率(Pmax),而对其他红树植物的Pmax没有显著影响;秋茄在45%光强下具有较高的Pmax,木榄的Pmax则在45%和30%光强下显著高于其他2个处理。随着生长光强的下降,秋茄幼苗叶片的光饱和点显著上升,木榄、老鼠簕和卤蕨的光补偿点呈下降趋势,木榄和卤蕨的表观量子效率升高的同时暗呼吸速率下降。木榄、老鼠簕和卤蕨具有较强的耐荫性,...     

Effect of salinity and waterlogging on growth,anatomical and antioxidative responses in <Emphasis Type="Italic">Mentha aquatica</Emphasis> L.

Salinity and waterlogging are two stresses which in nature often occur simultaneously. In this work, effects of combined waterlogging and salinity stresses are studied on the anatomical alteration, changes of enzymatic antioxidant system and lipid peroxidation in Mentha aquatica L. plants. Seedlings were cultured in half-strength Hoagland medium 50 days after sowing, and were treated under combination of three waterlogging levels (well drained, moderately drained and waterlogging) and NaCl (0, 50, 100, 150 mM) for 30 days. Moderately drained and waterlogging conditions induced differently aerenchyma formation in roots of M. aquatica salt-treated and untreated plants. Moreover, stele diameter and endodermis layer were also affected by salt stress and waterlogging. Salt stress significantly decreased growth, relative water content (RWC), protein level, catalase (CAT) and polyphenol oxidase (PPO) activities, and increased proline content, MDA content, H₂O₂ level and activities of superoxide dismutase (SOD), peroxidase (POX), and ascorbate peroxidase (APX). Waterlogging in salt-untreated plants increased significantly growth parameters, RWC, protein content, antioxidant enzyme activity, and decreased proline content, H₂O₂ and MDA levels. In salt-treated plant, waterlogging caused strong induction of antioxidant enzymes activities especially at severe stress condition. These results suggest M. aquatica is a waterlogging tolerant plant due to significant increase of antioxidant activity, membrane stability and growth under water stress. High antioxidant capacity under waterlogging can be a protective strategy against oxidative damage, and help to salt stress alleviation.     

5种红树科植物叶片的比较解剖及其生态适应研究

用石蜡切片法对红树（Rhizophora apiculata Bl.）、红海榄（R.stylosa Griff.）、秋茄（Kandelia candel(Linn.) Druce）、木榄（Bruguiera gymnorrhiza(Linn.) Savigny）和海莲（B.sexangula(Lour.) Poir.）等5种红树科植物的叶片进行解剖学的观察和研究,结果表明：5种红树科植物叶片的表皮均有厚的角质膜和下皮层,表皮和下皮层的细胞常含有单宁;上表皮无气孔器;栅栏组织多层;木质部非常发达。说明了红树科植物的叶片具有很强的耐旱能力;同属植物的叶片在解剖结构上有着相似的特征。     

Review of wheat improvement for waterlogging tolerance in Australia and India: the importance of anaerobiosis and element toxicities associated with different soils

Background and Aims

The lack of knowledge about key traits in field environments is a major constraint to germplasm improvement and crop management because waterlogging-prone environments are highly diverse and complex, and the mechanisms of tolerance to waterlogging include a large range of traits. A model is proposed that waterlogging tolerance is a product of tolerance to anaerobiosis and high microelement concentrations. This is further evaluated with the aim of prioritizing traits required for waterlogging tolerance of wheat in the field.

Methods

Waterlogging tolerance mechanisms of wheat are evaluated in a range of diverse environments through a review of past research in Australia and India; this includes selected soils and plant data, including plant growth under waterlogged and drained conditions in different environments. Measurements focus on changes in redox potential and concentrations of diverse elements in soils and plants during waterlogging.

Key Results

(a) Waterlogging tolerance of wheat in one location often does not relate to another, and (b) element toxicities are often a major constraint in waterlogged environments. Important element toxicities in different soils during waterlogging include Mn, Fe, Na, Al and B. This is the first time that Al and B toxicities have been indicated for wheat in waterlogged soils in India. These results support and extend the well-known interactions of salinity/Na and waterlogging/hypoxia tolerance.

Conclusions

Diverse element toxicities (or deficiencies) that are exacerbated during waterlogging are proposed as a major reason why waterlogging tolerance at one site is often not replicated at another. Recommendations for germplasm improvement for waterlogging tolerance include use of inductively coupled plasma analyses of soils and plants.Key words: Waterlogging, microelements, toxicity, redox potential, wheat, anaerobiosis

‘No grain is ever produced without water, but too much water tends to spoil the grain and inundation is as injurious to growth as dearth of water.’ Narada Smriti XI, 19; circa 3000 bc.‘Waterlogging’ is defined as a condition of the soil where excess water limits gas diffusion; while ‘waterlogging tolerance’ is defined as survival or the maintenance of high growth rates, biomass accumulation or grain yield under waterlogging relative to non waterlogged (usually drained soil) conditions (Setter and Waters, 2003).

     

Interactive effects of salinity and water depth on the growth of Melaleuca ericifolia Sm. (Swamp paperbark) seedlings

Melaleuca ericifolia Sm. (Swamp paperbark) is a common tree species in freshwater and brackish wetlands in southern and eastern Australia. The survival of this species in many wetlands is now threatened by increased salinity and inappropriate water regimes. We examined the response of 5-month-old M. ericifolia seedlings to three water depths (exposed, waterlogged and submerged) at three salinities (2, 49 and 60 dS m⁻¹). Increasing water depth at the lowest salinity did not affect survival, but strongly inhibited seedling growth. Total biomass, leaf area and maximum root length were highest in exposed plants, intermediate in waterlogged plants and lowest in submerged plants. Although completely submerged plants survived for 10 weeks at the lowest salinity, they demonstrated negative growth rates and were unable to extend their shoots above the water surface. At the higher salinities, M. ericifolia seedlings were intolerant of waterlogging and submergence: all plants died after 9 weeks at 60 dS m⁻¹. Soil salinities increased over time, and by Week 10, exceeded external water column salinities in both the exposed and waterlogged treatments. In exposed sediment, ∼90% of plants survived for 10 weeks at 60 dS m⁻¹ even though soil salinities reached ∼76 dS m⁻¹. No mortality occurred in the exposed plants at 49 dS m⁻¹, and small but positive relative growth rates were recorded at Week 10. We conclude that at low salinities M. ericifolia seedlings are highly tolerant of sediment waterlogging, but are unlikely to tolerate prolonged submergence. However, at the higher salinities, M. ericifolia seedlings are intolerant of waterlogging and submergence and died rapidly after 5 weeks exposure to this combination of environmental stressors. This research demonstrates that salinity may restrict the range of water regimes tolerated by aquatic plants.     

Effects of Waterlogging on Water Relations of Actively-growing and Dormant Sitka Spruce Seedlings

Two-year-old Sitka spruce [Picea sitchensis (Bong.) Carr.] seedlings,either actively growing or dormant, were waterlogged in a growthroom at 15 °C. Shoot and root growth, transpiration andleaf water potential were observed. In actively-growing plants shoot extension continued after waterlogging,though at a reduced rate, and shoots of dormant plants brokebud and extended during the waterlogging period. Root growthwas suppressed by waterlogging in both types of plant. The 22day waterlogging treatment eventually killed the actively-growingplants but plants which were dormant at the time of waterloggingwere more tolerant. Changes in plant water relations after waterloggingwere entirely different depending on the condition of the plantswhen the soil was flooded. Dormant plants showed a gradual reductionin transpiration and increased water stress over the waterloggingperiod; after the soil was drained leaf water potential increasedto equal the value of control plants which had been maintainedin a freely drained condition, but transpiration did not increaseuntil root growth began. Actively-growing plants exhibited amore complex behaviour, characterized by a very rapid reductionin transpiration after waterlogging, accompanied by a briefperiod of water stress, followed by a period of increasing transpirationrate in the absence of water stress. Finally a second reductionin transpiration occurred and water stress increased as theseedlings died. The importance of the stage of activity of theroot system to the response of plants to waterlogging is discussed. Picea sitchensis (Bong.) Carr., Sitka spruce, waterlogging, water relations, dormancy, transpiration, water potential     

The growth of Kandelia candel seedlings in mangrove habitats of the Zhangjiang estuary in Fujian, China

Propagules of Kandelia candel collected from the Zhangjiang estuary were planted in mangrove habitats along the intertidal gradient. The rooting rates of K. candel propagules varied spatially. The lowest rate occurred in Avicennia marina forest (69.7%). The rates were higher in K. candel forest (90.0%), at the fringe of the mangrove forest (89.3%) and on the bare tidal flat outside the mangrove forest (82.7%). After one year, the survival rates of seedlings planted under A. marina forest, K. candel forest, at the fringe of the mangrove forest, and on the bare tidal flat were 13.7%, 54.7%, 76.0%, and 34.7%, respectively. Among the surviving K. candel seedlings, those at the fringe of the mangrove forest and on the bare tidal flat had greater height, stem diameter, leaf number, leaf area, and biomass than those under A. marina and K. candel forests. These results demonstrated that establishment and growth of K. candel seedlings occurred successfully at the fringe of the mangrove forest, but were the worst under A. marina forest. The performance of K. candel seedlings was independent of physico-chemical characters of sediment. However, interspecies competition, propagule predation by insects and crabs, and the incident light had significant effects on seedling survival and growth.     

Soil salinity and pH in Japanese mangrove forests and growth of cultivated mangrove plants in different soil conditions

Soil conditions of mangrove forests in southern Japan were found to correlate largely with zonal distributions of the species.Kandelia candel grew in soils with low salinity and low pH,Avicennia marina, Rhizophora stylosa andSonneratia alba in soils with high salinity and high pH, andBruguiera gymnorrhiza in soil with a wide range of pH but limited range of salinity.Lumnitzera racemosa colonized soil with a wide range of pH and medium salinity. Seedlings ofKandelia candel, Bruguiera gymnorrhiza andRhizophora stylosa were planted in soils with differing salinity and pH. Optimum seedling growth ofKandelia, Bruguiera andRhizophora occurred when plants were cultivated in soils similar to those of their natural habitats, suggesting that growth of mangrove species and their zonal distributions were regulated by salinity and soil pH.     

Lipid composition of mangrove and its relevance to salt tolerance

Lipid compositions of mangrove trees were studied in relation to the salt-tolerance mechanism. Leaves and roots were obtained from seven mature mangrove trees on Iriomote Island, Okinawa: Bruguiera gymnorrhiza, Rhizophora stylosa, Kandelia candel, Lumnitzera racemosa, Avicennia marina, Pemphis acidula and Sonneratia alba. Lipids of mangrove leaves mainly consisted of 11 lipid classes: polar lipids, unknown (UK) 1–6, sterols, triacyl glycerols, wax ester and sterol ester (UK 3 and 4 were found to be tri-terpenoid alcohol in this study). Of these lipid classes, sterol ester was the main lipid in all species comprising 17.6–33.7% of total lipids. Analysis of the chemical structure found that the sterol esters mainly consisted of fatty acid esters of tri-terpenoid alcohols. One major tri-terpenoid alcohol was identified to be lupeol by interpretation of infrared resonance, nuclear magnetic resonance and mass spectrometry. Because of the unique anatomy of the mangrove root, lipid analyses were made separately for epidermis, cortex and innermost stele, respectively. The concentration of free tri-terpenoid alcohols showed a higher tendency in the outside part than in the inside portion of the roots, suggesting their protective roles. Relevance of lipid composition to salt tolerance was studied with propagules of K. candel and B. gymnorrhiza planted with varied salt concentrations. The proportions of free tri-terpenoids increased with salinity in both leaves and roots of K. candel, and only in roots of B. gymnorrhiza. No salt-dependent changes were noted in the phospholipid and fatty acid compositions in both species. These findings suggested that salt stress specifically modulated the terpenoid concentrations in mangroves. Electronic Publication     

Stem anatomical variations in seedlings of the mangrove Bruguiera gymnorrhiza grown under periodical waterlogging

The purpose of this study was to investigate the stem anatomical adaptations of the mangrove Bruguiera gymnorrhiza seedlings under experimental conditions that simulated semidiurnal tides. The inundation periods in these treatments were 0, 2, 4, 6, 8, 10 and 12 h. In the 0–6 h treatments, cortex thickness, pith radius and stem radius increased, but then declined when inundation period exceeded 6 h. Significant negative linear correlations were found between waterlogging duration and vessel element length, bar number per perforation plate and gelatinous fibre ratio. Whereas vessel density and fibre diameter showed only slight fluctuations, fibre cell wall thickness declined dramatically from 2 h treatments onwards, in contrast, vessel wall thickness increased under long-term waterlogging conditions (>6 h). Tangential vessel diameter and fibre length exhibited similar tendencies, first decreasing significantly with prolonged inundation, and then increasing under long-term waterlogging duration up to 6 h. These results indicated that the internal structure of B. gymnorrhiza seedlings was affected by periodical waterlogging. The distinct structural changes with short (<6 h) or long (> 6 h) term inundation suggest distinct strategies for maintaining a balance between growth, conductive capacity, conductive safety and mechanical strength.     

The effect of combined salinity and waterlogging on the halophyte Suaeda maritima: The role of antioxidants

Suaeda maritima is a halophytic plant and its habitat is salt marsh. In order to adapt to saline or waterlogged conditions, plants have evolved mechanisms that include antioxidant protection. However, the combined effect of salinity and waterlogging on antioxidants in S. maritima is unknown. The aim of this study was therefore to investigate the effect of saline-flooding on levels of glutathione and phenolic compounds (antioxidants) and the correlation between their concentration and activity in S. maritima shoots grown in their natural habitat and in a glasshouse.Shoots were collected from two different elevations (and so different degrees of flooding) of a salt marsh while other plants were grown in half strength seawater in the controlled conditions of a glasshouse for 8 weeks (drained and flooded). Shoot samples were used to measure dry weight, glutathione and its reduction state, malonyldialdehyde content (MDA), polyphenol content, superoxide anion and 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) scavenging activity in the shoots of S. maritima.Growth of S. maritima was greater in plants growing on the high marsh than at a lower elevation and in drained medium as opposed to waterlogged conditions in the glasshouse. Waterlogging caused an increase in glutathione and its reduction state. The glutathione half-cell redox potential (E_GSSG/2GSH) was more negative in plant shoots grown under waterlogged conditions than in plants grown under normal conditions. Higher DPPH and superoxide anion scavenging activity was associated with high antioxidant concentrations (glutathione and polyphenols).Conclusions. Under saline-flooded conditions in the field and in the glasshouse, plants produced a higher concentration of antioxidants than under drained conditions. These result indicated that antioxidant molecules play an important role in S. maritima plants under combined salinity and waterlogging stress.     

Comparison of adenosine metabolism in leaves of several mangrove plants and a poplar species

A possible increased demand for ATP in salt- tolerant mangrove plants was studied by the comparison of metabolic fates of [8-¹⁴C] adenosine in leaf disks of several mangrove plants and of poplar. In mangrove trees, Rhizophora stylosa, Bruguiera gymnorrhiza, Kandelia candel and Sonneratia alba, 56–92% of [8-¹⁴C]adenosine taken up by leaf disks was converted during 3 h incubation to salvage products, i.e., nucleotides and RNA. Synthesis of nucleotides including ATP was stimulated by salt stress induced by 250 mM NaCl. In leaf disks of Avicennia marina, a mangrove shrub that produces glycinebetaine as compatible solutes, 46% of radioactivity entered salvage products when [8-¹⁴C] adenosine was continuously supplied to the leaf disks. Hydrolysis of adenosine to adenine was extremely active in this mangrove shrub. This is probably due to the high activity of adenosine nucleosidase (EC 3.2.2.7). In leaf disks of another mangrove shrub, Lumnitzera racemosa, only limited amounts of [8-¹⁴C]adenosine were metabolised (< ca. 30% taken up by leaf disks), but synthesis of ATP and ADP was stimulated by salt stress. In Pemphis acidula leaf disks, adenosine salvage activity was low and more than 30% of adenosine was hydrolysed to adenine. In leaf disks of poplar, a non-salt-resistant plant, ca. 40% of [8-¹⁴C] adenosine was converted to salvage products during 3 h of incubation, but the rate was slightly reduced by treatment with 250 mM NaCl. The present results suggest that large mangrove trees generally have efficient adenosine salvage ability, which is stimulated by salt. Lesser salvage activity is found in small size mangrove shrubs, although salt generally still enhances salvage activity.     

强潮区较高纬度移植红树植物秋茄的生理生态特性

以中国红树林引种最北界的乐清湾西门岛海域为研究地点,选择黄零为1.96、1.66和1.35 m 3个高程断面(每个潮水周期平均淹水时间分别为3.18、3.65、4.07 h),研究了1年生和4年生秋茄的生长、叶片的光合色素和保护酶活性、植株可溶性糖含量、游离氨基酸含量、离子含量等指标的变化。结果表明,当滩涂高程为黄零1.66 m以上时,每个潮水周期平均淹水时间低于3.65 h,1年生和4年生秋茄幼苗均可生长;当滩涂高程为低于黄零1.35 m时,每个潮水周期平均淹水时间高于4.07 h,1年生秋茄幼苗仍能正常生长,而4年生秋茄叶片叶绿素、类胡萝卜素总量、茎叶中的可溶性总糖和游离氨基酸含量、过氧化物酶(POD)活性以及K+/Na+比均显著降低,同时,叶片中的丙二醛(MDA)和茎、叶中Na+含量均快速上升,导致了生长缓慢。总体上说,较大树龄秋茄可生长在高程为黄零1.66 m以上,其原因是植株在每个潮水周期平均淹水时间少于3.65 h时仍能够维持正常的碳氮代谢。     

Root morphology is related to the phenotypic variation in waterlogging tolerance of two populations of Suaeda salsa under salinity

The effects of waterlogging and salinity on seedling emergence, seedling growth and ion accumulation in a euhalophyte Suaeda salsa in an intertidal zone and on saline inland soil were investigated. Seedlings of S. salsa from the intertidal zone emerged more rapidly than those of the inland population under both waterlogged and drained conditions. Waterlogging and salinity had no adverse effects on seedling emergence of S. salsa from the intertidal zone, but markedly inhibited this parameter in the inland population. Waterlogging did not affect the seedling survival, shoot dry mass, and shoot height in high salinity in S. salsa from the intertidal zone, while the opposite trend was shown in the inland population. The root dry mass was higher in S. salsa from the intertidal zone as compared to the inland population, in waterlogged treatments by 1.9, 1.3, and 1.5 times in 1, 200, and 600 mM NaCl, respectively, and in drained treatments by 1.8, 2.3, and 3.0 times in 1, 200, and 600 mM NaCl, respectively. Waterlogging increased Na⁺ and K⁺ concentrations in high salinity, but waterlogging had no effect on Cl^- concentration in shoots of S. salsa from the intertidal zone. In all NaCl treatments, waterlogging had no effect on concentrations of these ions in shoots of S. salsa from the saline inland site. In a field investigation, the fresh mass of shoots and roots were lower, whereas the root/shoot ratio was 1.5 times higher in S. salsa from the intertidal zone, compared with the inland population. These findings indicate that S. salsa population from the intertidal zone is more waterlogging tolerant than the inland population. S. salsa from the intertidal zone produced relatively more root biomass and this might help anchor plants against tidal action in the intertidal zone. The physiological and morphological characteristics may determine the natural distributions of the two S. salsa populations in their different saline environments.     

Aerenchyma and an Inducible Barrier to Radial Oxygen Loss Facilitate Root Aeration in Upland, Paddy and Deep-water Rice (Oryza sativa L.)

The present study evaluated waterlogging tolerance, root porosityand radial O₂ loss (ROL) from the adventitious roots, of sevenupland, three paddy, and two deep-water genotypes of rice (Oryzasativa L.). Upland types, with the exception of one genotype,were as tolerant of 30 d soil waterlogging as the paddyand deep-water types. In all but one of the 12 genotypes, thenumber of adventitious roots per stem increased for plants grownin waterlogged, compared with drained, soil. When grown in stagnantdeoxygenated nutrient solution, genotypic variation was evidentfor root porosity and rates of ROL, but there was no overalldifference between plants from the three cultural types. Adventitiousroot porosity increased from 20–26 % for plants grownin aerated solution to 29–41 % for plants grown instagnant solution. Growth in stagnant solution also induceda ‘tight’ barrier to ROL in the basal regions ofadventitious roots of five of the seven upland types, all threepaddy types, and the two deep-water types. The enhanced porosityprovided a low resistance pathway for O₂ movement to the roottip, and the barrier to ROL in basal zones would have furtherenhanced longitudinal O₂ diffusion towards the apex, by diminishinglosses to the rhizosphere. The plasticity in root physiology,as described above, presumably contributes to the ability ofrice to grow in diverse environments that differ markedly insoil waterlogging, such as drained upland soils as well as waterloggedpaddy fields.     

The effect of temperature on salt uptake by tomato plants with diurnal and noctural waterlogging of salinized rootzones

Summary Tomato plants were grown at three constant temperatures (10, 20 and 28°C) with drained or waterlogged rootzones and were irrigated with saline solution (0.09M NaCl).Each increase in temperature resulted in an increase in leaf Na-ion and Cl-ion concentrations in plants grown with drained rootzones. However, with plants grown with waterlogged rootzones, maximum leaf concentrations of Na-ions and Cl-ions occurred at 20°C.At 10°C there were no differences between Na-ion and Cl-ion concentrations for drained or waterlogged treatments. At 20 and 28°C, waterlogging of the rootzone resulted in significantly higher concentrations of Na-ions and Cl-ions in leaf and stem tissues than occurred with drained rootzones.There were no differences in Na-ions and Cl-ions and Cl-ions in plant tops if plants were waterlogged with saline solution during the day or night.Transpiration increased significantly with each increase in temperature but showed no other treatment dependent responses.